Consumerist found this amazing list of retailer cost for Monster Cable, where many of the cables went for nearly double what they cost. Monster responded with an answer that was thoughtful from their point of view. Many times, in "jewellery, clothing, and furniture, the markup is even greater." Fine, I don't know anything about retail. But technically speaking and from a consumer's point of view, here is what I think:
While Monster cables are of good quality and engineering, when it comes to digital signals, specifically HDMI cables, we know that its a better idea to buy a $5 dollar HDMI cable today, and then when bandwidth requirements go up in future specs of HDMI, just buy another $5 cable then. It's a lot cheaper than $100 HDMI cables from Monster. The exceptions come when you are running long runs of cable through a wall, where swapping cables is annoying and the signal can degrade (yes, the digital signal can degrade, as proven here, here and here.)
When it comes to analog cables, like composite and speaker cables, I for one believe you can get a lot out of midrange (Monster is midrange compared to some cables I've seen and used) analog cabling that has a lot of shielding for interference. More than Radio Shack stock cable? I don't know. But I'm sure cable outlets like Monoprice have lower costs for similar cabling. Did you know Monster Cable has a garage with Lamborghini showcars and throws a huge celebrity bash at CES every year? Not cheap.
Not that Monster is alone in this industry. All cable makers who sell through home theater stores are going to have a big mark up.